Interactions

We know Emerald Ash Borer has a parasitic relationship with the Ash species but wouldn’t it be great if we could turn the tables and introduce a parasitic organism to Emerald Ash Borer?  Recently, in the summer of 2007, the U.S. Department of Agriculture in conjunction with the Animal and Plant Health Inspection Service (APHIS) and Forest Service began research determine if known effective parasitoid species of Emerald Ash Borer from China would work in reducing EAB populations here in the US.  Three “wasp” parasitoids were studied:  Spathius agrili, Oobius agrili, and Tetrastichus planipennisi.

Spathius agrili is a larva ectoparasitoid (effects host organism on external surface).  The wasp first detects the habitat of EAB from the volatile chemicals emitted by Ash species (EAB’s host).  Once in the proximity of EAB, the wasp can detect vibrations within the Ash tree, indicating the location of feeding larva.  From here, the wasp will lay its eggs on the EAB larva, the source of their development and nutrition.  Results in China reported a 90% parasite success rate for S. agrili.

Oobius agrili is an egg parasitoid which injects its own eggs in to recently laid EAB eggs.  From there the O. agrili develops and hatches, preventing the further development of EAB.  Not nearly as effective as S. agirli, results found 50% of EAB eggs with O. agrili eggs.

Tetrastichus planipennisi is a larva endoparasitoid (effects host organism internally).  This wasp will inject its eggs in the EAB larva which grow, eventually killing the larva.  The irony!  Similar to O. agrili, Tetrastichus planipennisi was found to infect 60% of EAB larva.

Although research suggests these wasps to be effective at combating the EAB dilemma, actions have still not been taken to implement the defense.  Before releasing a non-indigenous species into our environment, APHIS is responsible for determining how the species will interact with organisms other than those it is intended for.  Thus far, results have been promising as all three wasps have shown extremely specific selection, venturing to other alternatives rarely, if ever.  Finally, these species are referred to as wasps but they are far from what most typically associate with wasps.  These wasps are very tiny, usually smaller than sesame seeds; nearly microscopic.  Best of all, they DO NOT posses stingers harmful to humans.

Other parasitoids considered have been Atanycolus hicoriae, which is again a wasp type species that is a natural enemy of close relatives to EAB.  Studies have shown a parasitoid rate of approximately 20%.  Also, a microbial control approach has been taken using a pesticide derived from the GHA strain of the Beauveria bassiana fungus.  According to the Environmental Protection Agency,

“Many strains of  are found worldwide in the soil. They control insects by growing on them, secreting enzymes that weaken the insect's outer coat, and then getting inside the insect and continuing to grow, eventually killing the infected pest.”

Results from field studies vary, yielding infection rates ranging from 58.5% to 83% in EAB.